conversation-stopper
noun [ C usually singular ] uk/kɒn.vəˈseɪ.ʃənˌstɒp.ər/ us/kɑːn.vɚˈseɪ.ʃənˌstɑː.pɚ/
（因导致尴尬或惊讶而）打断谈话的言论
a remark that stops the natural flow of the conversation because it is unexpected and in some way causes embarrassment or shock
When she told us her son was in prison, it was a real conversation-stopper. 当她告诉我们她儿子入狱了之后，大家都停止了谈话。